Time division multiplex (TDM) architectures often demand data at high throughput sampling rates. Such architectures often use a low duty cycle optical ON/OFF switch with fast rise and fall times to generate a stream of pulses. Because of the high coherence of the laser source, leakage light caused by the incomplete turn-OFF of the optical switch can produce excessive phase noise at the receiver and drastically reduce the overall signal-to-noise ratio. This may be due to bleed-through light during the OFF time interval of a single optical source causing unwanted signal output from a plurality of sensors all driven by the light output from the same optical source. This may be a problem where there are a large number of optical light sources in the system producing stray and/or bleed-through light that contaminates the desired light signal traveling in an optical fiber in a given time slot in the TDM system.
The required ON/OFF attenuation ratio for an optical switch increases with the number of sensors driven by the light from a single optical source and with the number of laser sources that generate light beams that are switched through the fiber. For example, fiber optic acoustic sensor systems, such as using a plurality of Mach Zehnder interferometers, may operate from a light beam from a single laser source and employ a single fiber-optic “return” path where the output from each interferometer is time division multiplexed onto the return path. A plurality of multiplexed signals carried by a single fiber in such a system gives rise to the need for an optical switch with a significant OFF attenuation factor. For such a system using 64 sensors with 64 corresponding TDM light outputs, the required OFF attenuation for the switch is 60–75 dB to maintain a good signal to noise ratio. A known approach to achieve this requirement has been to use a pair of expensive lithium niobate electro-optic switches connected in series in order to achieve the needed OFF attenuation. There exists a need for a cost-effective way to provide optical switching that can satisfy the requirements of such a system.